* gthr-win32.h (__GTHREAD_HIDE_WIN32API): Test for non-zero
	value, not just if defined.

	* libstdc++-v3/config/os/mingw32/os_defines.h (__GTHREAD_HIDE_WIN32API):
	Define to 1 by defualt.
	(NOMINMAX): Define.

From-SVN: r67069